1. Field of the Invention
The present invention relates to monolithic ceramic electric components, laminated coil components, and methods of producing monolithic ceramic electric components.
2. Description of the Related Art
As a known monolithic ceramic electronic component, Japanese Unexamined Patent Application Publication No. 2002-252117, for example, discloses a laminated coil component. As shown in FIG. 6, a laminated coil component 201 includes inner ceramic green sheets 213 and 214 having conductive coil patterns 209 and 210 disposed on the respective surfaces, inner ceramic green sheets 215 having interlayer-connecting via holes 207, and outer ceramic green sheets 216. In general, the inner ceramic green sheets 213 to 215 and the outer ceramic green sheets 216 have the same thickness.
These ceramic green sheets 213 to 216 are laminated and compacted to form a laminate 221 shown in FIG. 7. The laminate 221 is then fired, and input-output external electrodes 222 and 223 are formed on the fired laminate 221.
The conductive coil patterns 209 and 210 are electrically connected in series through the interlayer-connecting via holes 207 to form a helical coil L10 inside the laminate 221. This laminated coil component 201 includes the helical coil L10 having a coil axis that is perpendicular to the lamination direction of the laminate 221, and the input-output external electrodes 222 and 223 electrically connected to both ends of the helical coil L10 and disposed at the left and the right sides of the laminate 221. Accordingly, the laminated coil component 201 is referred to as a “vertically laminated and horizontally wound” coil component.
Moreover, Japanese Unexamined Patent Application Publication No. 2002-134355 discloses a laminated electronic component including thick outer ceramic green sheets to produce outer layers having a predetermined thickness with a minimized number of sheets.
In general, the surfaces of the input-output external electrodes on the monolithic ceramic electronic components are plated with, for example, Ni and Sn for improving solderability.
However, when the input-output external electrodes 222 and 223 on the laminated coil component 201 are plated with, for example, Ni and Sn, improper plating of Ni or Sn sometimes occurs at undesirable portions of the laminated coil component 201. Specifically, as shown in FIG. 8, undesirable plating films 230 are deposited on the surfaces of the laminate 221 adjacent to the conductive coil patterns 209 and 210 that function as internal electrodes.
The cause of the improper plating is low insulating resistance between the surfaces of the laminate 221 and the conductive coil patterns 209 and 210. Therefore, in order to prevent the improper plating, the thicknesses of the outer layers including the outer ceramic green sheets 216 are set to 150 μm or more to increase the insulating resistance.
However, the diameter of the helical coil L10 must be maximized to achieve high impedance when the component is small in size. In other words, the number of inner ceramic green sheets 215 having interlayer-connecting via holes 207 must be maximized, whereas the outer layers must be minimized.